This invention relates to a cyclone particularly adapted for use in a dense medium separation process.
The expression xe2x80x9cdense medium separation processxe2x80x9d herein means separation of a particulate material into dense and less high gravity fractions at a predetermined cut point. In the process the particulate material is carried in a dense liquid medium which typically comprises a mixture of water and particles of dense material such as ferrosilicon or magnetite.
Conventional dense medium cyclones comprise a cylindrical inlet chamber into which raw material is fed tangentially, so that circular motion is imparted to the material in the chamber. A low gravity fraction or floats, are extracted from the inlet chamber through a vortex finder which extends into the inlet and which leads to an outlet direct chamber. A cone formation depends from the inlet chamber in a direction opposed to the vortex finder, and terminates at its remote end in an axially disposed outlet for the high gravity fraction or sinks. With cyclones of this type, the through put and performance is limited by the flow through the axial outlet. It is moreover not possible to increase the size of the outlet beyond a certain percentage of that of the vortex finder, because of design criteria. For many applications therefor, cyclones of this type are operated at a reduced feed rate, in order to obtain the required cut between the low gravity fraction and high gravity fraction.
It is accordingly an object of the present invention to provide a novel dense medium cyclone which it is believed will exhibit an improved throughput relative to conventional cyclones.
According to the present invention, a cyclone adapted for use in a dense medium separation process comprises an inlet chamber having a tangential raw material feed inlet, a vortex finder extending into the inlet chamber, and defining a low gravity fraction outlet for a low gravity fraction of separated material, a conical section opposed to the vortex finder extending and converging in a direction away from the inlet chamber, an outlet chamber extending co-axially with the conical section and in a direction opposed to the inlet chamber, and providing an unobstructed flow path to a high gravity fraction outlet for a high gravity fraction of separated material being disposed generally tangentially relative to the outlet chamber. It has been found that such an arrangement permits a greater volume of high gravity fraction to pass through the outlet in relation to the conventional cyclones described above.
In one arrangement according to the invention, a volute duct formation is provided adjacent the outlet chamber, such volute duct formation coupling the outlet chamber to the tangential high gravity fraction outlet thereof. Preferably, the volute duct formation will spiral outwardly from the conical section through about 180 degrees.
In one arrangement, the tubular section will preferably be of a constant diameter. Preferably the diameter of the tubular section will be substantially the same as that of the inlet chamber, although variations may be possible in this regard. Thus for example, an inwardly tapering conical section can be interposed between the inlet chamber and the tubular section. Alternatively, the tubular section could for example be in the form of a cone structure which converges from the inlet Head to the outlet thereof.
The invention further provides for the high gravity fraction outlet optionally to be throttled to provide a pressure drop across such outlet, if required. In a preferred arrangement, the ratio between the diameter of the inlet chamber and that of the high gravity fraction outlet will be in the order of 7.8. Thus, for a cyclone where an inlet chamber has a diameter of 660 mm, the high gravity fraction outlet will preferably have a diameter in the order of 85 mm.
Also according to the invention, the cyclone includes a vortex extractor downstream from the high gravity fraction outlet. Such vortex extractor could comprise a tangential extractor inlet to an extractor chamber, and an axially disposed outlet which could be throttled.
Also included within the scope of the invention is a method of separating liquid borne raw material into a low gravity fraction and a high gravity fraction in a dense medium separation process comprising the steps of providing a cyclone in accordance with the invention, introducing raw feed into the cyclone tangentially through the inlet into the inlet chamber to cause rotational movement thereof within the chamber, withdrawing a low gravity fraction of the material through the vortex finder, and withdrawing a high gravity fraction of material tangentially through the high gravity fraction outlet disposed towards the remote end of the outlet chamber.